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What is a Linear Actuator?

An electric linear actuator is a device that converts the rotational motion of a motor into linear motion – that is push and pull movements.

This way it is possible to lift, adjust, tilt, push or pull heavy or hard-to-reach objects, simply by pushing a button.

Additionally, actuators provide a safe, quiet and clean movement with accurate motion control. They are energy efficient and have a long lifetime with little or no maintenance.

Installing an actuator is very easy compared to hydraulic or pneumatic systems and it takes up much less space, as it has no pumps or hoses.

The ability of the actuators to adapt to specific needs ensures well-functioning solutions that are applied in many different aspects for a wide range of applications and products.

An electric linear actuator consists of a motor, a gear and a spindle including a nut. A special version of the linear actuator is the built-in actuator meant for integration in a customer guidance or linear column. A complete actuator system solution includes one or more linear actuators, a control box and a control device to operate the actuators.

What is a Lifting Column?

Lifting columns are designed to raise and lower to provide optimum ergonomics in a number of applications for the office, hospital & care sector and industrial markets. It is possible to connect a number of columns in parallel drive to provide electrical adjustability for heavy objects. The advantage of the column is that the linear guiding is built into the structure of the actuator and does not need adding externally.

Why use an Electric Linear Actuator?

Electric linear actuators are the perfect solution when you need simple, safe and clean movement with accurate and smooth motion control. You may choose actuator systems for adjustments, tilting, pushing, pulling and lifting with thrusts up to 10,000 N.

Actuators can be integrated into sophisticated control systems using data bus communication. You get precise position feedback and accurate variable control over acceleration and velocity.

Compared to both hydraulic and pneumatic systems an actuator solution is a lot easier to install. It takes up less space as there are no hoses and pumps that require routine maintenance to avoid safety hazards and messy oil leaks.

A linear actuator has a long lifetime with little or no maintenance at all. This ensures a very low total operating cost compared to other systems.

Electric actuator systems are quiet, clean, non-toxic and energy efficient. They fulfil the ever increasing demands and legislation concerning environmentally sound equipment.

What are some real world examples of what a Linear Actuator can do?

Linear actuators move things. Some examples of practical automation applications are: sand, salt, and fertilizer spreader chutes;  throttle control, marine engine hatch, slide out steps, hoppers, hidden doors, solar panels, sliding doors, sliding window treatments, farming implementations and animatronics. Industrial applications include, damper control and height adjustable work stations.

What is the difference between an Electric Actuator and an Hydraulic Actuator?

The hydraulic actuator uses fluid to push a ram backwards and forwards, where as an electric actuator uses a DC motor to drive a lead screw, the lead screw is fitted with a nut that runs up and down the lead screw converting rotary motion into linear motion.

What is the difference between Static Load and Dynamic Load?

Dynamic, working, or lifting load is the force that will be applied to the linear actuator while it is in motion. Static load, also called the holding load, is the force that will be applied to the linear actuator when it is not in motion.

In what direction can loads be applied to Linear Actuators?

Linear actuators can be used in tension, compression or combination applications. Eccentric and side loading should be avoided. Please consult technical catalogues to ensure that all hardware used in conjunction with the linear actuator can withstand the maximum restraining torque.

Are side loading and eccentric loading permissible on Linear Actuators?

Side loading, or radial loading is a force applied perpendicular to the linear actuator centreline. Eccentric loading is any force whose centre of gravity does not act through the longitudinal axis of the actuator. Both side loading and eccentric loading should always be avoided as they can cause binding and shorten the life of the linear actuator.

Can Linear Actuators have limit switches?

Linear actuators can be supplied with limit switches. The type of limit switches available varies with each product range, these include electro-mechanical, magnetic proximity and rotary cam. Limit switches (if fitted) are normally pre-set on actuators. Limit switches allow you the flexibility to set the limits of travel on your actuator to fit your particular application. The customer is responsible for properly setting the limit switch in the unit. If the limit switches are not set, or are improperly set, the unit may be damaged during operation. In addition, limit switches may require resetting if the translating tube of your linear actuator is rotated manually, as this will change the limit switch setting.

What type of motors do the Linear Actuators use?

Linear Actuators are available with AC or DC motor variants, however each range has preferred standard types.

The AC Motors will be either 220-240 VAC 1-phase motors, 220-240/380-415VAC 3-phase motors (50/60Hz) or 24VDC motors.

Are Linear Actuators available in different speeds?

Linear actuators are available in a variety of linear speeds and a standard list is detailed with each product.

What is the duty cycle capability of a Linear Actuator?

Duty cycle rating for a linear actuator is generally expressed as a percentage of “on time” (the ratio of on time to total time) or as distance travelled over a period of time. The duty cycle rating is expressed differently for different actuator types.

What type of mounting do the Linear Actuators have?

The linear actuators generally have a mounting option at the end of the ram and at the gearbox end of the actuator to allow a pivoting movement. There are a number of options, double clevis as standard, or clevis to trunnion. However all have multiple mounting options including clevis, trunnion, fork, top plate, base plate and threaded rod end.

What type of enclosures do the Linear Actuators have?

Linear Actuators are either IP54 (NEMA 3) or IP66 as standard.

Is back-driving possible in electro-mechanical Linear Actuators?

Unless otherwise stated back-driving is possible in all electric linear actuators. Actuators that use a ball screw are normally fitted with an electrical brake (typically motor mounted) to prevent the load from back-driving the actuator. Note if a machine screw actuator is considered self-locking, it may still back-drive if significant vibration and cyclic temperature variations are present. ACME screw or trapezoidal screw actuators would be considered to be self-locking.

Can a Linear Actuator be run into a hard stop?

Linear actuators are not recommended for use in applications where they can run into dead stops or can be jammed. Examples of jamming include over-travelling the limit switches and jamming the nut and screw internally at the extreme ends of the stroke or driving the actuator against an immovable object and thus overloading the actuator severely.

What are the common factors in the failure of a Linear Actuator?

Improper loading, failure to set limit switches, excessive duty and extreme environments may contribute to premature actuator failure.

Can two or more Linear Actuators be synchronised?

If actuators are run using a “Direct On-Line” (DOL) starting method then they can only be roughly synchronised for speed and position. Small differences in motor speed and actuator loading may cause the units to get out of synchronisation. The units cannot therefore be guaranteed to run in synchronisation. For exact synchronisation a closed loop control system is recommended. This can be achieved using AC motors with AC inverters or servo motors with a matched drive as part of a control solution. The speed and position feedback is typically provided by a potentiometer, incremental or absolute encoder. With DC motors a lead screw fitted encoder or a hall sensor can provide the closed loop feedback.

Are special paint finishes available?

Linear actuators can be supplied with alternative materials and/or paint specifications for high corrosive areas. These options include stainless steel, chrome plating, electro-nickel plating or epoxy paint.

Are the actuators lubricated for life?

Linear actuators are grease lubricated for the ram and gearbox assemblies. The actuators are greased for life except where a geared motor is fitted. This will need regular maintenance as detailed in the user guide.

Testing

Each actuator product range is fully tested to ensure long term reliability.

Climatic Test

In the climatic test the actuators are tested to operate in extreme temperatures as well as to endure rapid changes in temperature. In some tests the actuator has to withstand going from a +100°C environment to -30°C repeatedly and still maintain full functionality.

Weather protection Test

In the weather protection test the resistance to both dust and water is tested.

Chemical Test

The ability to handle relevant chemicals is tested by exposing the actuator to diesel, hydraulic oil, urea nitrogen, fertilisers, liquid lime etc.

Electrical Tests

All electrical parts are tested i.e. power supply, power and signals cables, control signals etc. Electrical immunity is tested according to industrial standards i.e. for radio noise, electrical discharge and burst.

Mechanical Tests

Vibration, shock and bump testing are all part of the testing process.

 

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